Liarozole is a benzimidazole compound that is currently under development for the treatment of malignant disease. Liarozole has been shown to raise endogenous levels of retinoic acid in animal models, probably by binding to the cytochrome P450 moiety of the 4-hydroxylase responsible for retinoic acid catabolism. This study will assess the effect of liarozole on the P450 system and markers of retinoid metabolism and effect in humans.